The present invention relates to a shatter jet nozzle and a method for disrupting the smelt flow from a smelt spout of a recovery boiler.
A recovery boiler, such as a soda recovery boiler, is typically used in the chemical recovery of sulfate and other sodium-based substances from pulp manufacturing processes. Organic substances dissolved in the waste liquor during digestion or other pulping processes are combusted in the recovery boiler to melt inorganic compounds, e.g., ash, in the waste liquor and generate steam. The melted inorganic compounds flow as a primarily liquid smelt to the bottom of the recovery boiler. The smelt flows from the bottom of the boiler along one or more cooled smelt spouts to a dissolving tank. In the dissolving tank, the smelt is dissolved by water or weak white liquor to produce soda lye, e.g., green liquor.
The hot smelt flow from the spout causes “banging” and explosions when the smelt falls into the cooler liquid in the dissolving tank. The temperature of the smelt is on the order of 750° Celsius (° C.) to 820° C. In contrast, the temperature of the green liquor (or weak white liquor) in the dissolving tank, containing mainly water, is on the order of 70° C. to 100° C. This dramatic temperature difference between the hot smelt flow and the much cooler green liquor contributes to the explosions and banging noises as the smelt hits and is instantly cooled by the green liquor.
The intensity of the explosive reactions of the smelt in the dissolving tank may be reduced and controlled by disrupting the smelt flow into small streams, droplets or pieces as the flow leaves the spout and before it hits the liquid in the dissolving tank. It is conventional to disrupt the smelt with jet streams, e.g., steam jets, discharged from nozzles at low or medium pressure steam. These nozzles are referred to as shatter jet nozzles because they shatter the flow of the smelt.
The shatter jet nozzle discharges a jet stream at a specific volume and rate designed to break-up the smelt flow expected during normal operation of the recover boiler. The smelt flows at a relatively uniform rate and volumetric flow during normal recovery boiler operation. Conventional shatter jet nozzles direct a jet stream at a rate and volume designed to disrupt the normal uniform rate and flow of smelt. Conventional shatter jet nozzles are coupled to a single steam source that provides a constant flow rate of steam to the nozzles. The rate of steam flow to the nozzle typically cannot be adjusted remotely, and is adjusted at or near the nozzle.
Variations can occur in the rate and volume of smelt flowing from a recovery boiler. During normal operation of the recovery boiler, the normal steam jets from the shatter jet nozzles are capable of disrupting the smelt flow and sufficiently reducing explosions in the dissolving tank. However, the recovery boiler may be operated in an upset condition resulting in heavy smelt flows. These heavy smelt flows may not be adequately disrupted by the jets from the shatter jet nozzle and the smelt may cause explosions from which hot smelt droplets may splatter from the tank. These excessive explosions of smelt can result in equipment damage and danger to personnel safety.